It is known to provide vibration exciters or shakers for exciting arbitrary objects such as the wall of a building or domestic or office furniture, see, for example U.S. Pat. No. 4,506,117 of Fresard. Often, such devices comprise a magnet assembly defining an annular gap, a coil assembly disposed in the annular gap, suspension means mounting the coil assembly for reciprocating movement in the annular gap, the device being arranged to be mounted to the surface of a member to be vibrated, for example a suspended ceiling tile, in the case of Fresard.